In various contexts, the temperature of a circuit, such as one formed on an integrated chip needs to be monitored and controlled in order to insure that the chip properly functions and is protected from overheating. Such an application arises, for example, where a personal computer (PC) processor chip needs to be monitored and controlled. When the temperature of the computer chip exceeds a certain threshold level, a cooling fan is turned on so as to provide the circulating air to cool the chip. One technique that has been developed utilizes a semiconductor pn junction formed on the chip. Excitation currents applied through the pn junction generate temperature related signals that can be used to determine the temperature of the chip.
Some ICs are sensed externally or remotely, and thus have external terminals for coupling an internal temperature sensor, comprising a pn junction, to a remote temperature sensing circuit. Other ICs are sensed internally, and thus have an on-chip temperature sensing circuit coupled directly to the IC's temperature sensor pn junction.
There are a number of ways to determine the temperature of a pn semiconductor junction, whether the pn semiconductor junction is sensed internally or externally. One known method involves sequentially applying two different DC currents to the pn junction, and measuring the voltage across the pn junction, for the respective currents. The difference between the voltage values is a function of the temperature of the sensed pn junction, and thus represents that temperature measurement.
This known two current sequence method described above may provide inaccurate results, because it fails to adequately compensate for a parasitic resistance that develops across the sensed pn junction. Such a parasitic resistance may include the internal resistance of the sensed diode device as well as resistance associated with paths connecting the sensing circuit to the sensed pn junction.
It should be noted that the pn junction can be formed in any one of a number of ways Accordingly as used herein, it should be understood that the term “diode” as described and illustrated in connection with detailed description of the drawings and as may be used in the claims to designate a pn junction, is not necessarily limited to a diode arrangement, but includes any pn junction such as a pn junction of a bipolar transistor.
Reference is made to U.S. Pat. No. 7,010,440 (Lillis et al.) and U.S. Pat. No. 7,083,328 (Johnson).